Lua与C++的一些交互

Lua调用C函数用的堆栈是临时的,调用结束之后就被销毁了.

C调用Lua函数时,C负责堆栈.

 

1、C++调用Lua

调用函数的通用方法:

int lua_general_call( lua_State* lua, const char* func, const char* fmt, ... )
{
    va_list vl;
    int narg, nres;
    int len;


    len = lua_gettop( lua );

    va_start( vl, fmt );

    lua_getglobal( lua, func );

    if ( !lua_isfunction( lua, -1 ) )
    {
        fprintf( stderr, "函数不存在!\n" );
        goto err_exit;
    }


    narg = 0;

    while ( *fmt )
    {
        switch ( *fmt++ )
        {
            case 'd':
                lua_pushinteger( lua, va_arg( vl, int ) );
                break;

            case 'f':
                lua_pushnumber( lua, va_arg( vl, double ) );
                break;

            case 's':
                lua_pushstring( lua, va_arg( vl, char* ) );
                break;

            case '>':
                goto endwhile;

            default:
                fprintf( stderr, "未知参数格式!\n" );
                goto err_exit;
        }

        narg ++;

        //栈上至少有一个空余,否则增长
        if ( !lua_checkstack( lua, 1 ) )
        {
            fprintf( stderr, "LUA栈空间不足!\n" );
            goto err_exit;
        }
    }

endwhile:

    nres = strlen( fmt );

    if ( lua_pcall( lua, narg, nres, 0 ) != 0 )
    {
        fprintf( stderr, "调用错误 --- [%s]\n", lua_tostring( lua, -1 ) );
        goto err_exit;
    }

    nres = -nres;

    while ( *fmt )
    {
        switch ( *fmt++ )
        {
            case 'd':
                if ( !lua_isnumber( lua, nres ) )
                {
                    fprintf( stderr, "结果格式不对!\n" );
                    goto err_exit;
                }

                *va_arg( vl, int* ) = ( int )lua_tointeger( lua, nres );
                break;

            case 'f':
                if ( !lua_isnumber( lua, nres ) )
                {
                    fprintf( stderr, "结果格式不对!\n" );
                    goto err_exit;
                }

                *va_arg( vl, double* ) = ( double )lua_tonumber( lua, nres );
                break;

            case 's':
                if ( !lua_isstring( lua, nres ) )
                {
                    fprintf( stderr, "结果格式不对!\n" );
                    goto err_exit;
                }

                strcpy( va_arg( vl, char* ), lua_tostring( lua, nres ) );
                break;

            default:
                fprintf( stderr, "未知结果格式!\n" );
                goto err_exit;
        }

        nres++;
    }

    va_end( vl );
    lua_settop( lua, len );

    return 0;

err_exit:
    va_end( vl );
    lua_settop( lua, len );
    return -1;
}

Lua经常做为配置文件用

通用方法:

#define MAX_CFG_LEN               256

//GUID生成
static const char* g_tmp_cfg_name = "TMP_GUID";

//此处cfg_name 类似于xx.xx.xx
int read_cfg( lua_State* lua, const char* cfg_name, char ctt[MAX_CFG_LEN] )
{
    int len;
    char str[MAX_CFG_LEN * 2];

    len = lua_gettop( lua );
    memset( str, 0, sizeof( str ) );
    snprintf( str, sizeof( str ), "%s = %s", g_tmp_cfg_name, cfg_name );

    if ( luaL_dostring( lua, str ) != 0 )
    {
        fprintf( stderr, "LUA内存不足或语法错误\n" );
        goto err_exit;
    }

    lua_getglobal( lua, g_tmp_cfg_name );

    if ( lua_type( lua, -1 ) == LUA_TNIL )
    {
        fprintf( stderr, "变量为空值\n" );
        goto err_exit;
    }

    snprintf( ctt, MAX_CFG_LEN, lua_tostring( lua, -1 ) );

    lua_settop( lua, len );
    return 0;

err_exit:
    lua_settop( lua, len );
    return -1;
}

一般方法

lua_getglobal(lua, "中文配置测试1");
lua_getfield(lua, -1, "基本配置"); //键是字符串
lua_pushstring(lua, "数据目录"); //任何键都可以
lua_gettable(lua, -2);
fprintf(stdout, "%s\n", lua_tolstring(lua, -1, NULL));

2、Lua调用C++(LuaCallDllTest1.so)

实质上,Lua载入SO的方式有两种:

-- 方式一
require("LuaCallDllTest1");
--[[此句等同于:
local reg_fn_tmp = package.loadlib("LuaCallDllTest1.so", "luaopen_LuaCallDllTest1");
reg_fn_tmp(); -- 此函数往往为注册函数,执行一次等于注册了一个函数集
--]]


-- 方式二
local TestFn = package.loadlib("LuaCallDllTest1.so", "lua_hello_fn");



-- 方式一等同于自动注册,方式二等同于手工注册.

C函数的撰写

int lua_add(lua_State* lua)
{
    int ret;

    if (lua_gettop(lua) != 2 || !lua_isnumber(lua, -1) || !lua_isnumber(lua, -2))
    {
        return 0;
    }

    ret = lua_tointeger(lua, -1) + lua_tointeger(lua, -2);
    lua_pushinteger(lua, ret);

    return 1;
}

int lua_avg(lua_State* lua)
{
    int i;
    int len;
    int sum;

    len = lua_gettop(lua);
    for (sum = 0, i = 1; i <= len; i ++)
    {
        if (!lua_isnumber(lua, i))
        {
            return 0;
        }
        sum += lua_tointeger(lua, i);
    }

    lua_pushinteger(lua, sum);
    lua_pushnumber(lua, (double)sum / len);

    return 2;
}

// 压入表,与上面一些代码是逆过程
int lua_table(lua_State* lua)
{
    lua_newtable(lua);


    // 下面三行适应任何键
    lua_pushstring(lua, "key1");
    lua_pushstring(lua, "Value1");
    lua_settable(lua, -3);

    // 下面二行只适应字符串键
    lua_pushinteger(lua, 66666);
    lua_setfield(lua, -2, "key2");

    {
        lua_newtable(lua);
        lua_pushnumber(lua, 3.1415926);
        lua_setfield(lua, -2, "key31");
    }
    
    lua_setfield(lua, -2, "subtable");

    return 1;
}


// 压入闭包
int _my_counter(lua_State *lua)
{
    int val;
    int dir;

    //取UPVALUE值
    val = lua_tointeger(lua, lua_upvalueindex(1));
    dir = lua_tointeger(lua, lua_upvalueindex(2));
    //把第一个UPVALUE值处理后压栈,该值用于返回
    if (dir == 0)
    {
        lua_pushinteger(lua, ++ val);
    }
    else
    {
        lua_pushinteger(lua, -- val);
    }
    
    //COPY该栈顶 该值用于更新UPVALUE
    lua_pushvalue(lua, -1);
    //弹出栈顶元素,覆盖第一个UPVALUE 即更新UPVALUE
    lua_replace(lua, lua_upvalueindex(1));
    return 1;
}

int lua_counter(lua_State *lua)
{
    int idx;
    int dir;

    //取初始值
    idx = lua_tointeger(lua, 1);
    //取方向
    dir = lua_tointeger(lua, 2);
    //UPVALUE入栈
    lua_pushinteger(lua, idx);
    lua_pushinteger(lua, dir);
    //指明闭包,指明UPVALUE个数
    lua_pushcclosure(lua, _my_counter, 2);
    return 1;
}

Lua调用上面相关函数

require("LuaCallDllTest1");

TLib = TestLuaCallLibName -- 在注册函数中注册的函数集名称

MSG = TLib.TestLuaCallMsg -- 一个显示函数,上面未列出

MSG('MSG From Lua');

MSG(TLib.TestLuaCallAdd(1, 2)..'')
MSG(TLib.TestLuaCallAvg(2, 7))

local t = TLib.TestLuaCallTable('Hello World!')

MSG(t.key1)
MSG(t.key2..'')
MSG(t.subtable.key31..'')



count1 = TLib.TestLuaCallCounter(25, 1)
MSG(count1())
MSG(count1())
MSG(count1())
MSG(count1())


count2 = TLib.TestLuaCallCounter(25, 0)
MSG(count2())
MSG(count2())
MSG(count2())
MSG(count2())